The concept of a tire inflation system has been implemented on military vehicles for many years. Many military vehicles are equipped with a central tire inflation system (CTIS) which incorporates both inflation and deflation features, allowing the pressure of the tire to be varied in response to the road conditions experienced by a vehicle. For example, on relatively soft terrain, the tires should be deflated somewhat to improve traction. In contrast, on harder surfaces, such as paved roads, the tires should be more highly pressurized; however, over-inflation can result in both uneven wear to the tires and damage to the road.
In contrast, commercial tire inflation systems for use on trucks and other commercial vehicles, such as those described in U.S. Pat. No. 5,584,949 to Ingram, are not necessarily designed to allow the operator to decrease or increase tire pressure based on the road conditions. Instead, their primary function is to ensure that tire pressure does not fall below a preset cold tire pressure. As tire pressure decreases, the area of the tire in contact with the road increases, increasing friction and fuel consumption. Because these commercial tire inflation systems are designed to maintain preset tire pressures, they can also decrease maintenance costs and increase the life of the tires and treads. They supply increased air pressure not only to tires which are experiencing a leak but also to tires which might only be experiencing a decrease in pressure resulting from normal use.
Most commercial air pressurization systems incorporate two elements: first, a sealable connection between a rotatable part and a stationary part and, second, means to transport air from a pressurized supply to the tire in need of increased air pressure. For example, in U.S. Pat. No. 5,287,906 to Stech, air is transported from the pressurized supply through a rigid tube which runs through the axle to a "T" connector located outside of the hub via a rotary union. Air is transported to the tires from hoses connected to the "T". Suitable rotary unions for Stech's invention are commercially available. Stech also describes an unloader valve which protects the air supply in the event of a blowout. Such valves are necessary for some pressurization systems because the pressurized air supply for the tire inflation system is typically the same as that for the brakes of the truck. In the event of a blowout, being able to stop the truck is a higher priority than maintaining the pressure in a heavily damaged tire.
The above-mentioned U.S. Pat. No. 5,584,949 to Ingram, describes an air inflation system in which the air is transported from the pressurized supply to the tire in part through the interior of the axle. The interior of the axle itself is pressurized. In this reference, tubing is connected to the pressurized axle via the hub to transport air from the inside of the axle to the tires.
In another example, U.S. Pat. No. 5,769,979 to Naedler describes a rotary air connection for the tire inflation system described in the '949 patent to Ingram. This connection includes a union between a stationary part and a rotatable part. The stationary part has a rotary seal, and the rotatable part includes a rigid tube extending through the stationary part and moveable in the rotary seal. The connection of the tube to the hubcap is a sealed swivel joint which allows the tube to move in response to misalignment of the rotatable and stationary parts of the union. The relative positions of the non-rotating axle and the rotating wheel are not fixed. As the vehicle moves, the axle and the wheel move with respect to one another in response to irregularities in the road. Improperly balanced tires or poor alignment of the wheel hub on the axle will also result in relative movement of the wheel and axle, and, as a result, the rotating and stationary parts of the union. However, the movement of the tube within the union imparts stress on the rotary seal and, over time, results in undue damage to the seal or even detachment of the tube from the connector.
Accordingly, it is an object of this invention to provide an axle and hub assembly for use with a tire pressurization system that allows for misalignment of the rotatable and stationary parts of the assembly while providing an improved rotary seal and sealing mechanism between the tire and the air pressure source.
It is a further object of this invention to provide an axle and hub assembly for use with a tire pressurization system which can be opened and repaired or undergo routine maintenance while mounted on the vehicle.
It is also an object of this invention to provide an axle and hub assembly for use with a tire pressurization system which includes safeguards to prevent damage to lubrication compartments in the wheel from excess pressure or particulate material in the axle.